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Discussion Starter · #1 ·
I'm going to start a thread on troubleshooting FCR's as I am having more than a little trouble with mine.
There are plenty of threads about the stock carbs, but not so much info on these Kehins.
There are a couple of jetting threads, but nothing on troubleshooting them.
I'm in the process of trying to figure out mine, but once I understand what is going on with them, I will post up a list of issues & fixes, so that anyone mad enough to want to keep playing with 660 based quads can have a better guide with regard to setup etc.

If you can, buy them new. I got mine 2nd hand, but wouldn't be buying another 2nd hand set in a hurry, think I will have spent everything I saved on parts & time before I'm through..........

Issues I have dealt with:

1/ They leaked out the fuel bowl like crazy.
The bowls had distorted slightly due to being over-tightened.
There were a couple of alignment dimples on the bowls, but the screws align them correctly anyway, so I filed the dimples down, then used a piece of 1200 grit wet & dry on a piece of glass to sand the mating faces of the bowls flat. Use plenty of CRC or similar product to keep the wet & dry clean & cutting the aluminium of the bowls nicely. Sit the glass on a stable wooden surface & tape the edges of the wet & dry down. Turn the bowls mating face down & start "sanding". turn the bowls thru 90deg regularly to ensure even pressure & cutting on all points. Quick spray of CRC each time (onto the wet & dry).
Keep going until you have a neat even mating surface

2/ The bowl gaskets had shrunk as well & wouldn't sit in the groves in the bowls. Soaking for about 1 hour in petrol made them swell up & back to shape. leave them too long & they will be too big, but drying for 10 min or so will bring them back.

Never over-tighten the screws, if there is a leak, over-tightening the screws will probably make it worse!

3/ Fuel was welling up out the main jet tube as soon as I turned the gas on.
Start with checking the floats for leaks, & the float jets & needles.

I found the float jets were 4mm, figure someone must have wanted to run alcohol in them.
For our sort of builds 2.8 - 3.2mm jets are indicated in the literature I have read.

Float height of 9mm from sealing face of carb body (measured when float is just holding needle seated, but spring not compressed) is the recommended starting place

So, this is where I'm at now.
175 mains
55 pilots
200 main air
pilot air screw 1.5 turns out
fuel screw 1 turn out
OCEMR needles

The carbs no longer leak, & they don't overflow when sitting statically with fuel turned on.
However I can't get the bike to run.

When I start it, it needs 1/2 - 2/3 throttle just to keep running.
The motor coughs & splutters & has a large haze of unburnt fuel "standing off" the inlet of the carbs.
when I turn the fuel off, the motor will slowly clear, & run clean for about 1/2 minute, before dying from fuel starvation.

I raised the float height (lowering the fuel level) in small steps & am now at 13mm from bottom of float to base of carb body, & only very little difference.

I have tried smaller main jets (went down to 165) but the motor runs worse when I turn the fuel off.

Seems to me I still have an issue with the fuel height in the float bowls first off, & then jet sizing etc can then be resolved.

Any thoughts/suggestions?

My build is 719cc (HR +4 crank & CP 13.5:1 102mm piston)
X4 cam
HV ported head
CT sonic pipe
39mm FCR's

Thanks
 

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Not sure about your specific problems, just chiming in on the "sanding" technique... It's good to have a full sheet of paper, emery cloth preferably. I find that making figure 8's works best... avoid straight line "back-and-forth" motion...the figure 8 is smooth and seamless. I've used this to take the glaze off clutch pressure plates, clean cyl heads etc.
 

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Discussion Starter · #3 ·
All good with that, I suggest wet & dry as it is finer than emery paper (1200 grit is suggested).
Weather you use figure 8's or straight line, turn the piece regularly was the point I wanted to make. This avoids any uneven pressure..........
 

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Discussion Starter · #4 ·

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Discussion Starter · #5 ·

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Discussion Starter · #6 ·
From what I can tell, these carbs were set up for alcohol.
Anyone have any bright ideas as to what may have been altered for this?

Maybe I should just go buy a drum of methanol.................
 

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Discussion Starter · #7 ·
ok, problems all solved.

Note to all & sundry:
Check the Emulsion Tubes.
These are supposedly all the same. They do not get changed for alcohol or gas.
The idea is you change the needles.
Whoever built these carbs drilled the emulsion tubes out.

Stock is 2.7mm. These were 3.2mm.
Now thats a BIG difference in cross-sectional area.
 

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From what I can tell, these carbs were set up for alcohol.
Anyone have any bright ideas as to what may have been altered for this?

Maybe I should just go buy a drum of methanol.................
If you end up with a set of carbs that was on alcohol then remove every jet along with the Main Nozzle and replace with new Keihin factory jets set up for your bike...you can't trust that the jets in your carb were not drilled out. you will find that everything rubber will need to be replaced (i.e. the slide seal, the pilot screw o ring and check the float seat and accelerator pump diaphragm).

My advice is to stay away from alcohol FCRs unless the person you buy them from knows how to set them completely back to Gas and assures there proper function. Let us know if you find the problem. Good luck
 

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Discussion Starter · #9 ·
Quick update, got to take the quad out for a frun in the dunes over the weekend.
Runs well & hauls ass!
I bought myself a wide-band O2 sensor & display (from Zealtronic) Wonderful piece of kit.
Dropped the mains back to 160's & needles on 2nd clip, midrange - top end was great.
Still need to tune the bottom end, but pretty happy when I can be cruising in top, knock it back to 4th & wheelie away from my friend on his LTR450

As blueranger said, every piece of rubber has now been replaced in these carbs, & the needle jets/emulsion tubes had been drilled.

The tuning guide I posted earlier is a great mine of information & gives great methodology for setting up carbs on any motor
 
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